Fuel cell

ABSTRACT

A fuel cell is provided with a separator that supports an electrolyte/electrode assembly sandwiched therebetween. The separator is provided with: first and second fuel gas supply parts in the center of which fuel gas supply holes are formed; first and second cross-link parts connected to the first and second fuel gas supply parts; and first and second sandwiching support parts connected to the first and second cross-link parts. Each first sandwiching support part is provided with a set of fuel gas exhaust passages that discharge fuel gas that has gone through a fuel gas passage and been used. The cross-sectional areas of the fuel gas exhaust passages are larger on the downstream sides than on the upstream sides, in terms of the direction of fuel gas flow.

TECHNICAL FIELD

The present invention relates to a fuel cell formed by sandwichingelectrolyte electrode assemblies between separators. Each of theelectrolyte electrode assemblies includes an anode, a cathode, and anelectrolyte interposed between the anode and the cathode.

BACKGROUND ART

Typically, a solid oxide fuel cell (SOFC) employs an electrolyte ofion-conductive oxide such as stabilized zirconia. The electrolyte isinterposed between an anode and a cathode to form an electrolyteelectrode assembly (MEA). The electrolyte electrode assembly isinterposed between separators (bipolar plates). In use, predeterminednumbers of the electrolyte electrode assemblies and the separators arestacked together to form a fuel cell stack.

For example, in a flat plate type solid oxide fuel cell disclosed inJapanese Laid-Open Patent Publication No. 10-172594, a separator la asshown in FIG. 17 is provided, and a plurality of unit cells (not shown)and separators la are stacked alternately. Gas supply holes 2 aa, 3 aa,and gas discharge holes 2 ab, 3 ab extend through four corners of theseparator la in the stacking direction, and a plurality of gas flowgrooves 4 aa and ridges 4 ab in a plurality of rows are arrangedalternately along the surface of the separator 1 a.

The gas flow grooves 4 aa are connected to the gas supply hole 2 aa andthe gas discharge hole 2 ab through triangular recesses 5 aa, 5 ab. Athrottle section 6 a and blocks 7 a are provided in a gas inlet sectionof the triangular recess 5 aa, near the gas supply hole 2 aa, as meansfor limiting the flow rate of the gas. The throttle section 6 a and theblocks 7 a function to increase the pressure loss of the gas flowingfrom the gas supply hole 2 aa to the gas inlet section for equaldistribution of the gas.

Further, at opposite ends of the gas flow grooves 4 aa, a shallow gasflow inlet section 8 aa and a shallow gas flow outlet section 8 ab areprovided to cause a pressure loss in the gas flow.

Further, in a solid oxide fuel cell disclosed in Japanese Laid-OpenPatent Publication No. 2005-085520, as shown in FIG. 18, the fuel cellis formed by stacking power generation cells 1 b, fuel electrode currentcollectors 2 b, air electrode current collectors 3 b, and separators 4b. The power generation cell 1 b includes a fuel electrode layer, and anair electrode layer, and a solid electrolyte layer interposed betweenthe fuel electrode layer and the air electrode layer. The fuel electrodecurrent collector 2 b is provided outside the fuel electrode layer, andthe air electrode current collector 3 b is provided outside the airelectrode layer. The separators 4 b are provided outside the currentcollectors 2 b, 3 b. Though not shown, a ring shaped metal cover coversthe outer circumferential portion of a circular porous metal body makingup the current collector 2 b, and a large number of gas outlets areprovided over the entire circumferential side portion of the cover atpredetermined intervals.

In the structure, the fuel gas diffused in the porous metal body isprevented from being emitted from the entire outer circumferentialportion of the porous metal body. According to the disclosure, theamount of the fuel gas which is not used in the power generation anddischarged from the outer circumferential portion is suppressed, and thefuel gas is thus supplied to the power generation cell 1 b efficiently.

Further, in a flat stack fuel cell disclosed in Japanese Laid-OpenPatent Publication No. 2006-120589, as shown in FIG. 19, a separator 1 cstacked on a power generation cell is provided. The separator 1 c isformed by connecting left and right manifold parts 2 c and a part 3 cdisposed at the center where the power generation cell is provided, byjoint parts 4 c. The joint parts 4 c have elasticity.

The manifold parts 2 c have gas holes 5 c, 6 c. One gas hole 5 c isconnected to a fuel gas channel 7 c, and the other gas hole 6 c isconnected to an oxygen-containing gas channel 8 c. The fuel gas channel7 c and the oxygen-containing gas channel 8 c extend in a spiral patterninto the part 3 c, and are opened to a fuel electrode current collectorand an air electrode current collector (not shown), respectively, atpositions near the center of the part 3 c.

SUMMARY OF INVENTION

In Japanese Laid-Open Patent Publication No. 10-172594, since seals areprovided, in comparison with seal-less structure, excessive loads tendto be applied to the MEAS. Therefore, for example, the MEAS may becracked or damaged undesirably. Further, Japanese Laid-Open PatentPublication No. 10-172594 is not directed to a technique of suitablypreventing the fuel gas, the oxygen-containing gas, or the exhaust gasfrom unnecessarily flowing around.

Further, in Japanese Laid-Open Patent Publication No. 2005-085520, thering-shaped metal cover has a large number of gas outlets formed atpredetermined intervals over the entire circumferential side portion ofthe metal cover, and the metal cover and the separator are provided asseparate components. Therefore, a larger number of components arerequired, the structure is complicated, and the cost is high. Further, alarger number of assembling steps are required, and thus, the operatingefficiency is low. Further, the dimension in the thickness direction islarge, and the length of the entire stack in the stacking direction islarge.

Further, in Japanese Laid-Open Patent Publication No. 2006-120589, thefuel gas, the oxygen-containing gas, or the exhaust gas tends to flowaround to portions to which such a gas does not need to be supplied. Asa result, the electrodes may be degraded undesirably, and powergeneration performance may be lowered undesirably. Further, in thisstructure, one power generation cell is provided for each separator 1 c,and the manifolds are provided outside while the MEA is centrallypositioned. Thus, the heat by the power generation tends to radiate andto reduce heat efficiency, which cannot facilitate thermallyself-sustaining operation.

The present invention solves the above problems, and an object of thepresent invention is to provide a fuel cell having simple and economicalstructure, in which it is possible to prevent gases from unnecessarilyflowing around to some portions, improve durability and heat efficiency,and facilitate thermally self-sustaining operation.

The present invention relates to a fuel cell formed by stackingelectrolyte electrode assemblies and separators alternately in astacking direction. Each of the electrolyte electrode assembliesincludes an anode, a cathode, and an electrolyte interposed between theanode and the cathode.

Each of the separators includes a sandwiching section for sandwichingthe electrolyte electrode assembly, a bridge connected to thesandwiching section, and a fuel gas supply section connected to thebridge. A fuel gas channel for supplying a fuel gas along an electrodesurface of the anode of one electrolyte electrode assembly and anoxygen-containing gas channel for supplying an oxygen-containing gasalong an electrode surface of the cathode of the other electrolyteelectrode assembly are individually formed in the sandwiching section. Afuel gas supply channel for supplying the fuel gas to the fuel gaschannel is formed in the bridge. A fuel gas supply passage extendsthrough the fuel gas supply section in the stacking direction forsupplying the fuel gas to the fuel gas supply channel.

The sandwiching section includes a fuel gas inlet for supplying the fuelgas to the fuel gas channel, an outer circumferential protrusionprotruding toward the fuel gas channel, and contacting an outercircumference of the anode, and at least one fuel gas outlet channelprovided adjacent to a portion connecting the sandwiching section andthe bridge for discharging the fuel gas partially consumed in the fuelgas channel (hereinafter referred to as the exhaust fuel gas). In thefuel gas outlet channel, the cross sectional area on the downstream sidein the gas flow direction of the fuel gas is larger than the crosssectional area on the upstream side in the gas flow direction of thefuel gas.

In the present invention, the separator includes the sandwichingsections for sandwiching the electrolyte electrode assemblies, thebridges connected to the sandwiching sections, and the fuel gas supplysection connected to the bridges. In the structure, the tightening loadin the stacking direction is not transmitted between the fuel gas supplysection and the electrolyte electrode assembly through the bridge. Thus,with simple and compact structure, a relatively large load is applied tothe portion requiring high sealing performance, and a relatively smallload is applied to the electrolyte electrode assembly. Accordingly,damage of the electrolyte electrode assembly is prevented, and powergeneration and collection of electrical energy are performedefficiently.

Further, the fuel gas supplied from the fuel gas inlet to the fuel gaschannel is prevented from blowing to the outside by the outercircumferential protrusion protruding toward the fuel gas channel tocontact the outer circumference of the anode. Therefore, the fuel gascan be utilized effectively by the power generation reaction, and thefuel utilization ratio is improved suitably.

Further, gases other than the fuel gas, such as the oxygen-containinggas and the exhaust gas do not flow around to the anode from the outsideof the electrolyte electrode assembly. Therefore, degradation in thepower generation efficiency due to oxidation of the anode is prevented,and improvement in the durability of the separator and the electrolyteelectrode assembly is achieved easily.

Further, after the fuel gas supplied from the fuel gas inlet to the fuelgas channel is partially consumed in the reaction, the partiallyconsumed fuel gas is discharged through at least one fuel gas outletchannel provided adjacent to the portion connecting the sandwichingsection and the bridge. Therefore, the fuel gas flowing through the fuelgas supply channel and the fuel gas supply passage of the fuel gassupply section of the bridge can be heated by the exhaust fuel gasbeforehand. Thus, thermally self-sustaining operation is facilitated.

Further, the fuel gas supplied from the fuel gas inlet to the fuel gaschannel is discharged through the fuel gas outlet channel. The crosssectional area of the fuel gas outlet channel is large on the downstreamside. In the structure, blowing of the fuel gas to the outside isprevented. Therefore, the fuel gas can be utilized effectively in thepower generation reaction, and the fuel utilization ratio is improvedsuitably.

Further, gases other than the fuel gas, such as the oxygen-containinggas and the exhaust gas do not flow around to the anode from the outsideof the electrolyte electrode assembly. Therefore, degradation in thepower generation efficiency due to oxidation of the anode is prevented,and improvement in the durability of the separator and the electrolyteelectrode assembly is achieved easily.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view schematically showing a fuel cell stackformed by stacking a plurality of fuel cells according to a firstembodiment of the present invention;

FIG. 2 is a cross sectional view showing the fuel cell stack, takenalong a line II-II shown in FIG. 1; FIG. 3 is an exploded perspectiveview showing the fuel cell;

FIG. 4 is a partially exploded perspective view showing gas flows in thefuel cell; FIG. 5 is a partial view showing a separator of the fuelcell;

FIG. 6 is a cross sectional view schematically showing operation of thefuel cell;

FIG. 7 is an exploded perspective view showing a fuel cell according toa second embodiment of the present invention;

FIG. 8 is a partial view showing a separator of the fuel cell;

FIG. 9 is an exploded perspective view showing a fuel cell according toa third embodiment of the present invention;

FIG. 10 is a partial view showing a separator of the fuel cell;

FIG. 11 is an exploded perspective view showing a fuel cell according toa fourth embodiment of the present invention;

FIG. 12 is an exploded perspective view showing a fuel cell according toa fifth embodiment of the present invention;

FIG. 13 is a partially exploded perspective view showing gas flows inthe fuel cell:

FIG. 14 is a partial view showing a separator of the fuel cell;

FIG. 15 is a cross sectional view showing the separator, taken along aline XV-XV in FIG. 14;

FIG. 16 is an exploded perspective view showing a fuel cell according toa sixth embodiment of the present invention;

FIG. 17 is a view showing a separator of a fuel cell disclosed inJapanese Laid-Open Patent Publication No. 10-172594;

FIG. 18 is a partially cross sectional view showing a fuel celldisclosed in Japanese Laid-Open Patent Publication No. 2005-085520; and

FIG. 19 is a view showing a separator of a fuel cell disclosed inJapanese Laid-Open Patent Publication No. 2006-120589.

DESCRIPTION OF EMBODIMENTS

As shown in FIGS. 1 and 2, a fuel cell according to a first embodimentof the present invention is formed by stacking a plurality of fuel cells10 in a direction indicated by an arrow A. The fuel cell 10 is a solidoxide fuel cell (SOFC) used in various applications, includingstationary and mobile applications. For example, the fuel cell 10 ismounted on a vehicle.

As shown in FIGS. 3 and 4, the fuel cell 10 includes electrolyteelectrode assemblies (MEAs) 26. Each of the electrolyte electrodeassemblies 26 includes a cathode 22, an anode 24, and an electrolyte(electrolyte plate) 20 interposed between the cathode 22 and the anode24. For example, the electrolyte 20 is made of ion-conductive oxide suchas stabilized zirconia. The electrolyte electrode assembly 26 has acircular disk shape. A barrier layer (not shown) is provided at least atthe outer circumferential edge of the electrolyte electrode assembly 26for preventing entry or discharge of the oxygen-containing gas and thefuel gas.

The fuel cell 10 is formed by sandwiching a plurality of (e.g., four)electrolyte electrode assemblies 26 between a pair of separators 28. Thefour electrolyte electrode assemblies 26 are provided on a circle arounda fuel gas supply passage 30 extending through the center of theseparators 28.

As shown in FIG. 3, each of the separators 28 is formed by joining afirst plate 28 a and a second plate 28 b made of, for example, a metalplate of stainless alloy, etc., or a carbon plate. A first fuel gassupply section 32 is formed in the first plate 28 a, and the fuel gassupply passage 30 centrally extends through the first fuel gas supplysection 32. Four first bridges 34 extend radially outwardly from thefirst fuel gas supply section 32 at equal angular intervals, e.g., 90°.The first fuel gas supply section 32 is integral with first sandwichingsections 36 each having a relatively large diameter through the firstbridges 34. The centers of the first sandwiching sections 36 are equallydistanced from the center of the first fuel gas supply section 32.

Each of the first sandwiching sections 36 has a circular disk shape,having substantially the same dimensions as the electrolyte electrodeassembly 26. The first sandwiching sections 36 are separated from eachother. A fuel gas inlet 38 for supplying the fuel gas is formed at thecenter of the first sandwiching section 36, or at a position deviatedupstream from the center of the first sandwiching section 36 in the flowdirection of the oxygen-containing gas.

Each of the first sandwiching sections 36 has a fuel gas channel 40 on asurface 36 a which contacts the anode 24, for supplying a fuel gas alongan electrode surface of the anode 24. Further, a pair of fuel gas outletchannels 42 a, a pair of fuel gas outlet channels 42 b, and a pair offuel gas outlet channels 42 c for discharging the fuel gas partiallyconsumed in the fuel gas channel 40 and a circular arc wall (detourchannel forming wall) 44 contacting the anode 24 and forming a detourpath to prevent the fuel gas from flowing straight from the fuel gasinlet 38 to the fuel gas outlet channels 42 a, 42 b, 42 c are providedon the surface 36 a of the first sandwiching section 36.

As shown in FIG. 5, the fuel gas outlet channels 42 a, 42 b, 42 c areprovided adjacent to a portion connecting the first sandwiching section36 and the first bridge 34, on both sides of the first bridge 34 atequal intervals. In the fuel gas outlet channels 42 a, 42 b, 42 c, thecross sectional area on the downstream side in the gas flow direction ofthe fuel gas along the fuel gas channel 40 is larger than the crosssectional area on the upstream side in the gas flow direction of thefuel gas.

Specifically, an outer circumferential protrusion 46 and a plurality ofprojections 48 are provided on the surface 36 a of each firstsandwiching section 36. The outer circumferential protrusion 46protrudes toward the fuel gas channel 40 to contact the outercircumferential portion of the anode 24, and the projections 48 contactthe anode 24. The fuel gas outlet channels 42 a, 42 b, 42 c are formedat the outer circumferential protrusion 46 by directly cutting outportions of the outer circumferential protrusion 46.

In the fuel gas outlet channels 42 a, 42 b, 42 c, the width H2 on theouter side of the outer circumferential protrusion 46 is larger than thewidth H1 on the inner side of the outer circumferential protrusion 46(H1<H2). The depth of the fuel gas outlet channels 42 a, 42 b, 42 c isthe same over the entire surfaces of the fuel gas outlet channels 42 a,42 b, 42 c. Thus, the cross sectional area on the downstream side in thegas flow direction is larger than the cross sectional area on theupstream side in the gas flow direction.

As shown in FIG. 3, the circular arc wall 44 has a substantiallyhorseshoe shape (circular arc shape with partial cutout). The fuel gasinlet 38 is provided inside the circular arc wall 44. The projections 48are made of, e.g., solid portions formed by etching or hollow portionsformed by press forming.

The first sandwiching section 36 has a pair of extensions 50 forcollecting electricity generated in the power generation of theelectrolyte electrode assembly 26, and for measuring the state of theelectrolyte electrode assembly 26. The extensions 50 protrude from theouter circumferential portion of the first sandwiching section 36 orfrom between the fuel gas outlet channels 42 a, 42 b.

As shown in FIGS. 3 and 6, each of the first sandwiching sections 36 hasa substantially planar surface 36 b which contacts the cathode 22. Asecond plate 28 b is fixed to the surface 36 b, e.g., by brazing,diffusion bonding, laser welding, or the like.

As shown in FIG. 3, a second fuel gas supply section 52 is formed in thesecond plate 28 b, and the fuel gas supply passage 30 extends throughthe center of the second fuel gas supply section 52. A predeterminednumber of reinforcement bosses 53 are formed on the second fuel gassupply section 52. Four second bridges 54 extend radially from thesecond fuel gas supply section 52. Each of the second bridges 54 has afuel gas supply channel 56 connecting the fuel gas supply passage 30 ofthe second fuel gas supply section 52 to the fuel gas inlet 38. The fuelgas supply channel 56 is formed, for example, by etching or by pressforming.

Each of the second bridges 54 is integral with a second sandwichingsection 58 having a relatively large diameter. A plurality ofprojections 60 are provided on the second sandwiching section 58, e.g.,by etching or press forming. The projections 60 form anoxygen-containing gas channel 62 for supplying an oxygen-containing gasalong an electrode surface of the cathode 22 on the surface 36 b of thefirst sandwiching section 36. The projections 60 function as a currentcollector (see FIGS. 3 and 6).

As shown in FIG. 6, an oxygen-containing gas supply passage 68 isconnected to the oxygen-containing gas channel 62 for supplying theoxygen-containing gas from a space between an inner circumferential edgeof the electrolyte electrode assembly 26 and an inner circumferentialedge of the first and second sandwiching sections 36, 58 in a directionindicated by an arrow B. The oxygen-containing gas supply passage 68extends inside the first and second sandwiching sections 36, 58 in thestacking direction indicated by the arrow A, between the respectivefirst and second bridges 34, 54 to form an oxygen-containing gas supplysection.

An insulating seal 70 for sealing the fuel gas supply passage 30 isprovided between the separators 28. For example, mica material, ceramicmaterial or the like, i.e., crustal component material, glass material,or composite material of clay and plastic may be used for the insulatingseal 70. The insulating seal 70 seals the fuel gas supply passage 30from the electrolyte electrode assemblies 26.

In the fuel cell 10, exhaust gas discharge passages 72 are providedaround the first and second sandwiching sections 36, 58. The exhaust gasdischarge passages 72 form an exhaust gas discharge section fordischarging the fuel gas and the exhaust gas partially consumed in theelectrolyte electrode assemblies 26 as an exhaust gas in the stackingdirection. As necessary, an air regulating plate 73 is provided in eachspace between the first and second sandwiching sections 36, 58 (see FIG.3).

As shown in FIGS. 1 and 2, a fuel cell stack 12 includes a first endplate 74 a having a substantially circular disk shape at one end in thestacking direction of the fuel cells 10. Further, the fuel cell stack 12includes a plurality of second end plates 74 b and a fixing ring 74 c atthe other end in the stacking direction of the fuel cells 10, through apartition wall 75. Each of the second end plates 74 b has a smalldiameter and a substantially circular shape, and the fixing ring 74 chas a large diameter and a substantially ring shape. The partition wall75 prevents diffusion of the exhaust gas to the outside of the fuelcells 10. The number of the second end plates 74 b is four,corresponding to the positions of the stacked electrolyte electrodeassemblies 26.

The first end plate 74 a and the fixing ring 74 c include a plurality ofholes 76. Bolts 78 are inserted into the holes 76 and bolt insertioncollar members 77, and screwed into nuts 80. By the bolts 78 and thenuts 80 through which the bolts 78 are screwed, the first end plate 74 aand the fixing ring 74 c are fixedly tightened together.

One fuel gas supply pipe 82, a casing 83, and one oxygen-containing gassupply pipe 84 are provided at the first end plate 74 a. The fuel gassupply pipe 82 is connected to the fuel gas supply passage 30. Thecasing 83 has a cavity 83 a connected to the respectiveoxygen-containing gas supply passages 68. The oxygen-containing gassupply pipe 84 is connected to the casing 83, and to the cavity 83 a.

A support plate 92 is fixed to the first end plate 74 a through aplurality of bolts 78, nuts 88 a, 88 b, and plate collar members 90. Afirst load applying unit 94 for applying a tightening load to the firstand second fuel gas supply sections 32, 52 and second load applyingunits 98 for applying a tightening load to each of the electrolyteelectrode assemblies 26 are provided between the support plate 92 andthe first end plate 74 a. The first load applying unit 94 and the secondload applying units 98 form a load applying mechanism.

The first load applying unit 94 includes a presser member 100 providedat the center of the fuel cells 10 (centers of the first and second fuelgas supply sections 32, 52) for preventing leakage of the fuel gas fromthe fuel gas supply passage 30. The presser member 100 is provided nearthe center of the four second end plates 74 b for pressing the fuelcells 10 through the partition wall 75. A first spring 104 is providedat the presser member 100 through a first receiver member 102 a and asecond receiver member 102 b. A front end of a first presser bolt 106contacts the second receiver member 102 b. The first presser bolt 106 isscrewed into a first screw hole 108 formed in the support plate 92. Theposition of the first presser bolt 106 is adjustable through a first nut110.

Each of the second load applying units 98 includes a third receivermember 112 a at the second end plate 74 b, corresponding to each of theelectrolyte electrode assemblies 26. The third receiver member 112 a ispositioned on the second end plate 74 b through a pin 114. One end of asecond spring 116 contacts the third receiver member 112 a and the otherend of the second spring 116 contacts a fourth receiver member 112 b. Afront end of a second presser bolt 118 contacts the fourth receivermember 112 b. The second presser bolt 118 is screwed into a second screwhole 120 formed in the support plate 92. The position of the secondpresser bolt 118 is adjustable through a second nut 122.

Operation of the fuel cell stack 12 will be described below.

As shown in FIG. 1, the fuel gas is supplied through the fuel gas supplypipe 82 connected to the first end plate 74 a. Then, the fuel gas flowsinto the fuel gas supply passage 30. The air as the oxygen-containinggas is supplied from the oxygen-containing gas supply pipe 84 to each ofthe oxygen-containing gas supply passages 68 through the cavity 83 a.

As shown in FIG. 6, the fuel gas flows along the fuel gas supply passage30 of the fuel cell stack 12 in the stacking direction indicated by thearrow A. The fuel gas moves through the fuel gas supply channel 56 ofeach fuel cell 10 along the surface of the separator 28.

The fuel gas flows from the fuel gas supply channel 56 into the fuel gaschannel 40 through the fuel gas inlet 38 formed in the first sandwichingsection 36. The fuel gas inlet 38 is provided at substantially thecentral position of the anode 24 of each electrolyte electrode assembly26. Thus, the fuel gas is supplied from the fuel gas inlet 38 tosubstantially the center of the anode 24, and flows along the fuel gaschannel 40 from substantially the central region to the outercircumferential region of the anode 24.

The air (oxygen-containing gas), which has been supplied to theoxygen-containing gas supply passages 68, flows from the space betweenthe inner circumferential edge of the electrolyte electrode assembly 26and the inner circumferential edges of the first and second sandwichingsections 36, 58 into the oxygen-containing gas channel 62 in thedirection indicated by the arrow B. In the oxygen-containing gas channel62, the air flows from the inner circumferential edge (center of theseparator 28) of the cathode 22 to the outer circumferential edge (outercircumferential edge of the separator 28) of the cathode 22, i.e., fromone end to the other end of the cathode 22 of the electrolyte electrodeassembly 26.

Thus, in each of the electrolyte electrode assemblies 26, the fuel gasflows from the center to the outer circumferential side on the electrodesurface of the anode 24, and the air flows in one direction indicated bythe arrow B on the electrode surface of the cathode 22. At this time,oxide ions flow through the electrolyte 20 toward the anode 24 forgenerating electricity by chemical reactions.

The exhaust gas chiefly containing the air after partial consumption inthe power generation reaction is discharged from the outercircumferential region of each of the electrolyte electrode assemblies26, and flows through the exhaust gas discharge passage 72 as the offgas, and the off gas is discharged from the fuel cell stack 12 (see FIG.1).

In the first embodiment, the separator 28 includes the first and secondsandwiching sections 36, 58 for sandwiching the electrolyte electrodeassemblies 26, the first and second bridges 34, 54 connected to thefirst and second sandwiching sections 36, 58, and the first and secondfuel gas supply sections 32, 52 connected to the first and secondbridges 34, 54.

Thus, the tightening load in the stacking direction is not transmittedbetween the first and second fuel gas supply sections 32, 52 and theelectrolyte electrode assemblies 26. With simple and compact structure,a relatively large load is applied to the portion requiring high sealingperformance, and a relatively small load is applied to the electrolyteelectrode assemblies 26. Thus, damages of the electrolyte electrodeassemblies 26 are prevented, and power generation and collection ofelectrical energy are performed efficiently.

The outer circumferential protrusion 46 which contacts the outercircumferential portion of the anode 24 is provided on the surface 36 aof the first sandwiching section 36. Therefore, after the fuel gas issupplied from the fuel gas inlet 38 to the fuel gas channel 40, blowingof the fuel gas to the outside is prevented. Therefore, the fuel gas canbe utilized effectively by the power generation reaction, and the fuelutilization ratio is improved suitably.

Further, gases other than the fuel gas, such as the oxygen-containinggas and the exhaust gas do not flow around to the anode 24 from theoutside of the electrolyte electrode assembly 26. Therefore, degradationin the power generation efficiency due to oxidation of the anode 24 isprevented, and improvement in the durability of the separator 28 and theelectrolyte electrode assembly 26 is achieved easily.

Further, in the surface 36 a of the first sandwiching section 36, thefuel gas outlet channels 42 a, 42 b, 42 c are provided adjacent to theportion connecting the first sandwiching section 36 and the first bridge34, on both sides of the first bridge 34. Therefore, the fuel gas issupplied from the fuel gas inlet 38 to the fuel gas channel 40, and thefuel gas is partially consumed in the reaction. Then, the fuel gas isdistributed into the fuel gas outlet channels 42 a, 42 b, 42 c, anddischarged separately.

Therefore, in the cathode surface of the separator 28, the water vaporand the unconsumed fuel gas are not concentrated in a certain region(central portion), and thus, degradation of the performance due to theshortage in the supply of the oxygen-containing gas is preventedsuitably. Accordingly, it becomes possible to achieve a uniformtemperature distribution in the fuel cell 10, and the durability of thefuel cell 10 is improved advantageously.

Further, the fuel gas flowing through the fuel gas supply passage 30 andthe fuel gas supply channel 56 can be heated by the exhaust fuel gasbeforehand. Thus, thermally self-sustaining operation is facilitated.

Further, in the fuel gas outlet channels 42 a, 42 b, 42 c, the width H2on the outer side of the outer circumferential protrusion 46 is largerthan the width H1 on the inner side of the outer circumferentialprotrusion 46 (H1<H2). Thus, in the fuel gas outlet channels 42 a, 42 b,42 c, the cross sectional area on the downstream side in the gas flowdirection is larger than the cross sectional area on the upstream sidein the gas flow direction. In the structure, blowing of the fuel gas tothe outside is prevented. Thus, the fuel gas is utilized effectively inthe power generation reaction, and improvement in the fuel utilizationratio is achieved advantageously.

Further, gases other than the fuel gas, such as the oxygen-containinggas and the exhaust gas do not flow around to the anode 24 from theoutside of the electrolyte electrode assembly 26. Therefore, degradationin the power generation efficiency due to oxidation of the anode 24 isprevented, and improvement in the durability of the separator 28 and theelectrolyte electrode assembly 26 is achieved easily.

Further, in the first embodiment, as shown in FIG. 3, the circular arcwall 44 is provided in the path connecting the fuel gas inlet 38 and thefuel gas outlet channels 42 a to 42 c on the surface 36 a of the firstsandwiching section 36 of the separator 28. The circular arc wall 44contacts the anode 24 of the electrolyte electrode assembly 26, andthus, improvement in the electricity collecting efficiency is obtained.

In the structure, the fuel gas supplied from the fuel gas inlet 38 tothe fuel gas channel 40 is blocked by the circular arc wall 44. Thus,the fuel gas does not flow straight from the fuel gas inlet 38 to thefuel gas outlet channels 42 a to 42 c. The fuel gas flows around in thefuel gas channel 40, and the fuel gas flows along the anode 24 over alonger distance. That is, the fuel gas flows along the anode 24 over alonger period of time, and the fuel gas can be consumed effectively inthe power generation reaction. Accordingly, the fuel gas utilizationratio is improved effectively.

Further, the fuel gas outlet channels 42 a to 42 c are formed by slitsor the like formed in the outer circumferential protrusion 46.Therefore, the structure is simplified comparatively. Further, reductionin the production cost and reduction in the number of components areachieved.

Further, the first and second fuel gas supply sections 32, 52 areprovided at the central part of the separator 28, and the plurality of,e.g., four electrolyte electrode assemblies 26 are arranged on a circlearound the first and second fuel gas supply sections 32, 52. In thestructure, the fuel gas and the oxygen-containing gas supplied to thefuel cells 10 (fuel cell stack 12) are heated suitably in heat producedby reaction of the remaining fuel gas discharged from the fuel gasoutlet channels 42 a, 42 b, 42 c into the oxygen-containing gas supplypassage 68 and the oxygen-containing gas flowing through theoxygen-containing gas supply passage 68. Thus, the heat efficiency isimproved, and thermally self-sustaining operation is facilitated in thefuel cell 10 (and the fuel cell stack 12).

Further, the fuel gas can be distributed uniformly to each of theelectrolyte electrode assemblies 26 from the first and second fuel gassupply sections 32, 52. Thus, improvement and stability in the powergeneration performance are achieved in each of the electrolyte electrodeassemblies 26.

Further, the first and second sandwiching sections 36, 58 have a shapecorresponding to the electrolyte electrode assemblies 26, and the firstand second sandwiching sections 36, 58 are separated from each other.Since the first and second sandwiching sections 36, 58 have a shape,e.g., circular disk shape corresponding to the electrolyte electrodeassemblies 26, it becomes possible to efficiently collect electricalenergy generated in the electrolyte electrode assemblies 26.

Further, since the first and second sandwiching sections 36, 58 areseparated from each other, it becomes possible to absorb variation ofthe load applied to the respective electrolyte electrode assemblies 26due to dimensional differences in the electrolyte electrode assemblies26 and the separators 28. Thus, the undesired distortion does not occurin the entire separators 28. It is possible to apply the load equally toeach of the electrolyte electrode assemblies 26.

Further, thermal distortion or the like of the electrolyte electrodeassemblies 26 is not transmitted to the adjacent, other electrolyteelectrode assemblies 26, and no dedicated dimensional variationabsorbing mechanisms are required between the electrolyte electrodeassemblies 26. Thus, the electrolyte electrode assemblies 26 can beprovided close to each other, and the overall size of the fuel cell 10can be reduced easily.

Further, the first and second bridges 34, 54 extend radially outwardlyfrom the first and second fuel gas supply sections 32, 52 such that thefirst and second bridges 34, 54 are spaced at equal angular intervals.In the structure, the fuel gas can be supplied from the first and secondfuel gas supply sections 32, 52 equally to the respective electrolyteelectrode assemblies 26 through the first and second bridges 34, 54.Thus, improvement and stability in the power generation performance canbe achieved in each of the electrolyte electrode assemblies 26.

Further, in the separator 28, the number of the first and secondsandwiching sections 36, 58 and the number of the first and secondbridges 34, 54 correspond to the number of the electrolyte electrodeassemblies 26. Therefore, the fuel gas is uniformly supplied from thefirst and second fuel gas supply sections 32, 52 to each of theelectrolyte electrode assemblies 26 through the first and second bridges34, 54 and the first and second sandwiching sections 36, 58. Thus,improvement and stability in the power generation performance can beachieved in each of the electrolyte electrode assemblies 26.

Further, the projections 48 provided on the first sandwiching section 36protrude toward the fuel gas channel 40, and contact the anode 24. Inthe structure, electrical energy is collected suitably through theprojections 48.

Further, the projections 60 provided on the second sandwiching section58 protrude toward the oxygen-containing gas channel 62, and contact thecathode 22. In the structure, electrical energy is collected suitablythrough the projections 60.

Further, the first sandwiching section 36 has the extensions 50. In thestructure, for example, electrical energy generated in the powergeneration of the electrolyte electrode assembly 26 can be collected,and a state such as the temperature of the electrolyte electrodeassembly 26 can be measured easily, through the extensions 50.

Further, the extensions 50 are provided at the outer circumference ofthe first sandwiching section 36, between the fuel gas outlet channels42 a, 42 b. In the structure, the extensions 50 are displaced frompositions directly exposed to the exhaust fuel gas. Thus, overheating bythe hot exhaust fuel gas is suppressed. The temperature measurement orthe like of the separator 28 or the electrolyte electrode assembly 26 isperformed highly accurately.

Further, since the fuel cell 10 has the exhaust gas discharge sectionwhere the exhaust gas discharge passage 72 extends in the stackingdirection and the oxygen-containing gas supply section having theoxygen-containing gas supply passage 68 for supplying theoxygen-containing gas before supplied to the electrolyte electrodeassembly 26, the overall size of the fuel cell 10 is reduced easily.

Moreover, the first and second fuel gas supply sections 32, 52 areprovided at the center of the separator 28, and the plurality of, e.g.,four oxygen-containing gas supply passages 68 are arranged on a circlearound the first and second fuel gas supply sections 32, 52. Further,the oxygen-containing gas supply passages 68 are arranged between theplurality of, e.g., four first and second bridges 34, 54. In thestructure, the fuel gas supplied to the fuel cells 10 (fuel cell stack12) can be heated suitably by heat produced in power generation. Thus,the heat efficiency is improved, and thermally self-sustaining operationis facilitated in the fuel cell 10 (and the fuel cell stack 12).

The fuel gas supplied to and partially consumed in the electrolyteelectrode assembly 26 is discharged through the fuel gas outlet channels42 a, 42 b, 42 c to the oxygen-containing gas supply passage 68. In thestructure, the oxygen-containing gas before consumption is heated byreaction with unconsumed fuel gas remaining in the exhaust fuel gas, andimprovement in the heat efficiency is achieved.

Further, the fuel cell 10 is a solid oxide fuel cell. With simplestructure, the oxygen-containing gas and the exhaust gas can beprevented from flowing around to the anode 24. Further, the exhaust gasis distributed to achieve a uniform temperature distribution. Thus, itis possible to improve durability of the fuel cell 10 (fuel cell stack12) and facilitate thermally self-sustaining operation.

In the first embodiment, the three fuel gas outlet channels 42 a, 42 b,42 c are provided on each of both sides of the first bridge 34, adjacentto the portion connecting the first sandwiching section 36 and the firstbridge 34. However, the present invention is not limited in thisrespect. For example, two or more fuel gas outlet channels may beprovided on each of both sides of the first bridge 34. Preferably, thearea where the fuel gas outlet channels are formed is within a range of180° of each of the first sandwiching sections 36 on the innercircumferential side of the separator (see FIG. 5). In this respect,preferably, the range of the fuel gas outlet channels is limited by theair regulating plate 73.

Further, the separator 28 is made of the first plate 28 a and the secondplate 28 b. For example, the second plate 28 b may be formed of twopieces, i.e., a circular plate and a cross-shaped plate.

FIG. 7 is an exploded perspective view showing a fuel cell 140 accordingto a second embodiment of the present invention. The constituentelements that are identical to those of the fuel cell 10 according tothe first embodiment are labeled with the same reference numerals, anddescriptions thereof will be omitted. Also in third and otherembodiments as described later, the constituent elements that areidentical to those of the fuel cell 10 according to the first embodimentare labeled with the same reference numerals, and descriptions thereofwill be omitted.

The fuel cell 140 includes separators 142, and the separator 142 isformed by joining a first plate 142 a and a second plate 142 b together.A pair of fuel gas outlet channels 144 a, a pair of fuel gas outletchannels 144 b, and a pair of fuel gas outlet channels 144 c areprovided on a surface 36 a of each of first sandwiching sections 36 ofthe first plate 142 a. A fuel gas partially consumed in the fuel gaschannel 40 is discharged through the fuel gas outlet channels 144 a, 144b, 144 c.

The fuel gas outlet channels 144 a, 144 b, 144 c are provided adjacentto a portion connecting the first sandwiching section 36 and the firstbridge 34, on both sides of the first bridge 34 at equal intervals. Inthe fuel gas outlet channels 144 a, 144 b, 144 c, the cross sectionalarea on the downstream side in the gas flow direction of the fuel gasalong the fuel gas channel 40 is larger than the cross sectional area onthe upstream side in the gas flow direction of the fuel gas.

The gas flow directions indicated by arrows C at the fuel gas outletchannels 144 a, 144 b, 144 c intersect straight lines connecting thefirst fuel gas supply section 32 and the fuel gas outlet channels 144 a,144 b, 144 c (see FIG. 8).

In the second embodiment, the oxygen-containing gas flows in directionsindicated by the arrows B, and the gas flow directions at the fuel gasoutlet channels 144 a, 144 b, 144 c are the directions indicated by thearrows C. The directions indicated by the arrows B and the directionsindicated by the arrows C intersect each other. In the structure, it ispossible to prevent gases other than the fuel gas, such as theoxygen-containing gas and the exhaust gas from flowing around to theanode 24 from the outside of the electrolyte electrode assembly 26.Therefore, degradation in the power generation efficiency due tooxidation of the anode 24 is prevented, and improvement in thedurability of the separator 142 and the electrolyte electrode assembly26 is achieved.

Therefore, thanks to the negative pressure effect by the flow of theoxygen-containing gas, the exhaust fuel gas is discharged smoothly fromthe fuel gas outlet channels 144 a, 144 b, 144 c. In the structure,efficient operation can be performed advantageously.

FIG. 9 is an exploded perspective view showing a fuel cell 150 accordingto a third embodiment of the present invention.

In the fuel cell 150, oxygen-containing gas supply passages 68 arepositioned outside around the first and second sandwiching sections 36,58. A plurality of exhaust gas discharge passages 72 are arranged on acircle around the first and second fuel gas supply sections 32, 52. Eachof the exhaust gas discharge passages 72 is provided between the firstand second bridges 34, 54. That is, the oxygen-containing gas issupplied in directions indicated by arrows D (in directions opposite tothe directions indicated by the arrows B) from the outside of the firstand second sandwiching sections 36, 58, and the oxygen-containing gas isdischarged to the exhaust gas discharge passages 72 on the center sideof the separator, inside the first and second sandwiching sections 36,58.

The fuel cell 150 includes separators 152, and each of the separators152 is formed by joining a first plate 152 a and a second plate 152 btogether. A pair of fuel gas outlet channels 154 a, a pair of fuel gasoutlet channels 154 b, and a pair of fuel gas outlet channels 154 c areprovided on a surface 36 a of each of first sandwiching sections 36 ofthe first plate 152 a. A fuel gas partially consumed in the fuel gaschannel 40 is discharged through the fuel gas outlet channels 154 a, 154b, 154 c.

The fuel gas outlet channels 154 a, 154 b, 154 c are provided adjacentto a portion connecting the first sandwiching section 36 and the firstbridge 34, on both sides of the first bridge 34 at equal intervals. Inthe fuel gas outlet channels 154 a, 154 b, 154 c, the cross sectionalarea on the downstream side in the gas flow direction of the fuel gasalong the fuel gas channel 40 is larger than the cross sectional area onthe upstream side in the gas flow direction.

The gas flow directions (indicated by arrows E) at the fuel gas outletchannels 154 a, 154 b, 154 c are the same directions as straight linesconnecting the first fuel gas supply section 32 and the fuel gas outletchannels 154 a, 154 b, 154 c (see FIG. 10).

In the third embodiment, the oxygen-containing gas flows along thecathode 22 from the outside of the first and second sandwiching sections36, 58 toward the first and second fuel gas supply sections 32, 52. Inthe structure, it is possible to prevent the other gases such as theoxygen-containing gas and the exhaust gas from flowing around to theanode 24 from the outside of the electrolyte electrode assembly 26.Thus, degradation of the power generation efficiency due to oxidation ofthe anode 24 is prevented, and improvement in the durability of theseparator 152 and the electrolyte electrode assembly 26 is achieved.

Further, the oxygen-containing gas flows in the directions indicated bythe arrows D, and the gas flow directions at the fuel gas outletchannels 154 a, 154 a, 154 c are the directions indicated by the arrowsE. In the structure, the directions indicated by the arrows D and thedirections indicated by the arrows E are the same. Thus, the sameadvantages as in the cases of the first and second embodiments areobtained. For example, thanks to the negative pressure effect by theflow of the oxygen-containing gas, the exhaust fuel gas is dischargedsmoothly through the fuel gas outlet channels 154 a, 154 a, 154 c.

Further, in the third embodiment, the exhaust gas discharge passages 72are arranged on a circle around the first and second fuel gas supplysections 32, 52. Further, each of the exhaust gas discharge passages 72is arranged between the first and second bridges 34, 54. In thestructure, the fuel gas supplied to the fuel cell 150 (and the fuel cellstack) is heated suitably by the heat generated by the power generationand the exhaust gas. Thus, the heat efficiency is improved, andthermally self-sustaining operation is facilitated.

Further, the fuel gas supplied to and partially consumed in theelectrolyte electrode assembly 26 is discharged to the exhaust gasdischarge passage 72 through the fuel gas outlet channels 154 a, 154 a,154 c. In the structure, by reaction of the unconsumed fuel gasremaining in the exhaust fuel gas and the unconsumed oxygen-containinggas, further heating of the exhaust gas is achieved, and improvement inthe heat efficiency is achieved.

Further, in the oxygen-containing gas channel 62, the oxygen-containinggas supplied to and partially consumed in the electrolyte electrodeassembly 26 is discharged to the exhaust gas discharge passage 72. Inthe structure, by reaction of the unconsumed fuel gas and the unconsumedoxygen-containing gas remaining in the exhaust gas, additional heatingof the exhaust gas is achieved, and improvement in the heat efficiencyis achieved.

FIG. 11 is an exploded perspective view showing a fuel cell 160according to a fourth embodiment of the present invention.

The fuel cell 160 includes a separator 162, and the separator 162 isformed by joining a first plate 162 a and a second plate 162 b together.Each of first sandwiching sections 36 of the first plate 162 a has aspiral wall 164 on the surface 36 a. A fuel gas inlet 38 is formedadjacent to the center of the spiral wall 164.

One fuel gas outlet channel 42 is formed on the surface 36 a adjacent toa portion connecting the first sandwiching section 36 and the firstbridge 34. In the fuel gas outlet channel 42, the cross sectional areaon the downstream side of the gas flow direction of the fuel gas alongthe fuel gas channel 40 is larger than the cross sectional area on theupstream side in the gas flow direction.

In the fourth embodiment, the fuel gas supplied into the fuel gaschannel 40 through the fuel gas inlet 38 is supplied to substantiallythe entire area in the surface 36 a by the guidance of the spiral wall164. Then, the fuel gas is discharged through the single fuel gas outletchannel 42. Thus, in the fourth embodiment, the same advantages as inthe cases of the first to third embodiments are obtained.

FIG. 12 is an exploded perspective view showing a fuel cell 170according to a fifth embodiment of the present invention.

The fuel cell 170 includes a separator 172, and the separator 172 isformed by joining a first plate 172 a and a second plate 172 b together.Each of first sandwiching sections 36 of the first plate 172 a has fuelgas outlet channels 174 a, 174 b for discharging the fuel gas partiallyconsumed in the fuel gas channel 40 (FIGS. 12 and 13).

A continuous outer circumferential protrusion 46 is formed in a surface36 a of each of the first sandwiching sections 36, and the fuel gasoutlet channels 174 a, 174 b include outlet holes 176 a, 176 b extendingthrough the first sandwiching section 36 at positions inside the outercircumferential protrusion 46 (see FIGS. 14 and 15).

Cover members 178 a, 178 b are fixed to a surface 36 b opposite to thesurface 36 a of the first sandwiching section 36. Each of the covermembers 178 a, 178 b has a substantially trapezoidal shape in a planview, and flanges 180 a, 180 b are provided on three sides excluding anopened front end. The outlet holes 176 a, 176 b are formed on thesurface 36 b of the first sandwiching section 36, and the flanges 180 a,180 b are fixed to the surface 36 b of the first sandwiching section 36such that the outlet holes 176 a, 176 b are positioned inside of theflanges 180 a, 180 b.

Channels 182 a, 182 b are formed between the cover members 178 a, 178 band the surface 36 b. Each of the channels 182 a, 182 b has one endconnected to the outlet hole 176 a or the outlet hole 176 b, and theother end opened to the outside. In the channels 182 a, 182 b, the crosssectional area is increased from the outlet holes 176 a, 176 b towardthe outside. The width H3 of the channels 182 a, 182 b at positionsadjacent to the outlet holes 176 a, 176 b side is smaller than the widthH4 of the channels 182 a, 182 b adjacent to the ends opened to theoutside (see FIG. 14).

As shown in FIG. 12, the second sandwiching section 58 of the secondplate 172 b has cutouts 184 a, 184 b for inserting the cover members 178a, 178 b on both sides of the second bridge 54.

In the fifth embodiment, after the fuel gas supplied from the fuel gasinlet 38 to the fuel gas channel 40 is partially consumed in thereaction, the partially consumed fuel gas moves toward the surface 36 bthrough the outlet holes 176 a, 176 b of the fuel gas outlet channels174 a, 174 a, and flows into the channels 182 a, 182 b formed in thecover members 178 a, 178 b. Further, the exhaust fuel gas flows throughthe channels 182 a, 182 b, and then, the exhaust fuel gas is dischargedfrom each opened end toward the oxygen-containing gas supply passage 68.

As described above, in the fifth embodiment, the fuel gas outletchannels 174 a, 174 b include the outlet holes 176 a, 176 b extendingthrough the first sandwiching sections 36 at positions inside the outercircumferential protrusion 46. In the structure, blowing of the fuel gasto the outside from the fuel gas channel 40 is prevented. Thus, the fuelgas is utilized effectively in the power generation reaction, andimprovement in the fuel utilization ratio is achieved advantageously.

Further, gases other than the fuel gas, such as the oxygen-containinggas and the exhaust gas do not flow around to the anode 24 from theoutside of the electrolyte electrode assembly 26. Therefore, degradationin the power generation efficiency due to oxidation of the anode 24 isprevented, and improvement in the durability of the separator 172 andthe electrolyte electrode assembly 26 is achieved easily.

Further, the fuel gas outlet channels 174 a, 174 b include the channels182 a, 182 b each having one end connected to the outlet hole 176 a orthe outlet hole 176 b, and the other end opened to the outside. In thechannels 182 a, 182 b, the cross sectional area is increased from theoutlet holes 176 a, 176 b toward the outside.

In the structure, gases other than the fuel gas, such as theoxygen-containing gas and the exhaust gas do not flow around to theanode 24 through the channels 182 a, 182 b from the outside of theelectrolyte electrode assembly 26. Therefore, degradation in the powergeneration efficiency due to oxidation of the anode 24 is prevented, andimprovement in the durability of the separator 172 and the electrolyteelectrode assembly 26 is achieved easily.

In the channels 182 a, 182 b, the width H4 at the end on the outer sideis larger than the width H3 on the inner side. Further, as necessary, asshown in FIG. 15, the dimension in the stacking direction on the outerside may be larger than the dimension in the stacking direction on theinner side. Further, one of the width and the dimension in the stackingdirection on the outer side may be larger than that on the inner side.

FIG. 16 is an exploded perspective view showing a fuel cell 190according to a sixth embodiment of the present invention.

The constituent elements that are identical to those of the fuel cell170 according to the fifth embodiment are labeled with the samereference numerals, and description thereof will be omitted.

The fuel cell 190 includes a separator 192, and the separator 192 isformed by joining a first plate 192 a and a second plate 192 b together.No circular arc wall is provided on the surface 36 a of each firstsandwiching section 36 of the first plate 192 a. A fuel gas inlet 38 isprovided at a position deviated toward the outside (in a directionspaced away from the center of the separator 192). In the second plate192 b, the fuel gas supply channel 56 extends outwardly beyond thecenter of the second sandwiching section 58 up to a positioncorresponding to the fuel gas inlet 38.

In the sixth embodiment, the fuel gas inlet 38 is provided deviatedoutwardly from the center of each first sandwiching section 36. In thestructure, without requiring the circular arc wall, the fuel gas flowingfrom the fuel gas inlet 38 to the fuel gas channel 40 is supplied to theentire surface of the fuel gas channel 40, and discharged to the fuelgas outlet channels 174 a, 174 b. Thus, in the sixth embodiment, thesame advantages as in the case of the fifth embodiment are obtained.

1. A fuel cell formed by stacking electrolyte electrode assemblies andseparators (alternately in a stacking direction, the electrolyteelectrode assemblies each including an anode, a cathode, and anelectrolyte interposed between the anode and the cathode, the separatorseach including: a sandwiching section for sandwiching the electrolyteelectrode assembly, a fuel gas channel for supplying a fuel gas along anelectrode surface of the anode of one electrolyte electrode assembly andan oxygen-containing gas channel for supplying an oxygen-containing gasalong an electrode surface of the cathode of another electrolyteelectrode assembly being individually formed in the sandwiching section;a bridge connected to the sandwiching section, a fuel gas supply channelfor supplying the fuel gas to the fuel gas channel being formed in thebridge; and a fuel gas supply section connected to the bridge, a fuelgas supply passage extending through the fuel gas supply section in thestacking direction for supplying the fuel gas to the fuel gas supplychannel, the sandwiching section including: a fuel gas inlet forsupplying the fuel gas to the fuel gas channel; an outer circumferentialprotrusion protruding toward the fuel gas channel, and contacting anouter circumference of the anode; and at least one fuel gas outletchannel provided adjacent to a portion connecting the sandwichingsection and the bridge for discharging the fuel gas partially consumedin the fuel gas channel, wherein, in the fuel gas outlet channel, across sectional area on a downstream side in a gas flow direction of thefuel gas is larger than a cross sectional area on an upstream side inthe gas flow direction of the fuel gas.
 2. The fuel cell according toclaim 1, wherein the sandwiching section further includes a detourchannel forming wall protruding toward the fuel gas channel to contactthe anode, the detour channel forming wall preventing the fuel gas fromflowing straight from the fuel gas inlet to the fuel gas outlet channel.3. The fuel cell according to claim 1, wherein the gas flow direction atthe fuel gas outlet channel intersects a direction of a straight lineconnecting the fuel gas supply section and the fuel gas outlet channel.4. The fuel cell according to claim 1, wherein the gas flow direction atthe fuel gas outlet channel is the same direction as a straight lineconnecting the fuel gas supply section and the fuel gas outlet channel.5. The fuel cell according to claim 1, wherein the fuel gas outletchannel has an outlet hole extending through the sandwiching sectioninside the outer circumferential protrusion.
 6. The fuel cell accordingto claim 5, wherein the fuel gas outlet channel is provided on a surfaceopposite to the anode, and includes a channel having one end connectedto the outlet hole, and another end opened to the outside; and the crosssectional area of the channel is increased from the outlet hole towardthe outside.
 7. The fuel cell according to claim 1, wherein the fuel gasoutlet channel is formed at the outer circumferential protrusion.
 8. Thefuel cell according to claim 1, wherein the fuel gas supply section isprovided at a center of the separator, and a plurality of theelectrolyte electrode assemblies are arranged on a circle around thefuel gas supply section.
 9. The fuel cell according to claim 1, whereinthe sandwiching section has a shape corresponding to each of theelectrolyte electrode assemblies, and a plurality of the sandwichingsections are separated from each other.
 10. The fuel cell according toclaim 1, wherein a plurality of the bridges extend radially outwardlyfrom the fuel gas supply section at equal angular intervals.
 11. Thefuel cell according to claim 1, wherein, in the separator, the numbersof the sandwiching sections and the bridges correspond to the number ofthe electrolyte electrode assemblies.
 12. The fuel cell according toclaim 1, wherein a plurality of projections protruding toward the fuelgas channel to contact the anode are provided on the sandwichingsection.
 13. The fuel cell according to claim 1, wherein a plurality ofprojections protruding toward the oxygen-containing gas channel tocontact the cathode are provided on the sandwiching section.
 14. Thefuel cell according to claim 1, wherein an extension for collectingelectrical energy generated in the electrolyte electrode assembly ormeasuring a state of the electrolyte electrode assembly is provided onat least one of the sandwiching sections.
 15. The fuel cell according toclaim 14, wherein the extension is provided on an outer circumference ofthe sandwiching section, between the fuel gas outlet channels.
 16. Thefuel cell according to claim 1, further including: an exhaust gasdischarge section made up of an exhaust gas discharge passage extendingin the stacking direction for discharging, as an exhaust gas, the fuelgas and the oxygen-containing gas supplied to the electrolyte electrodeassemblies and partially consumed by reaction in the electrolyteelectrode assemblies; and an oxygen-containing gas supply section madeup of an oxygen-containing gas supply passage extending in the stackingdirection for supplying the oxygen-containing gas to theoxygen-containing gas channel before the oxygen-containing gas issupplied to the electrolyte electrode assemblies.
 17. The fuel cellaccording to claim 16, wherein the fuel gas supply section is providedat a center of the separator, and a plurality of the oxygen-containinggas supply passages are arranged on a circle around the fuel gas supplysection, and the oxygen-containing gas supply passages are arrangedbetween a plurality of the bridges.
 18. The fuel cell according to claim17, wherein the fuel gas supplied to the electrolyte electrodeassemblies and partially consumed by reaction in the electrolyteelectrode assemblies, is discharged as an exhaust fuel gas through thefuel gas outlet channel to the oxygen-containing gas supply passages.19. The fuel cell according to claim 16, wherein the fuel gas supplysection is provided at a center of the separator, a plurality of theexhaust gas discharge passages are arranged on a circle around the fuelgas supply section, and the exhaust gas discharge passages are arrangedbetween a plurality of the bridges
 20. The fuel cell according to claim19, wherein the fuel gas supplied to and partially consumed in theelectrolyte electrode assemblies is discharged as an exhaust fuel gasthrough the fuel gas outlet channel to the exhaust gas dischargepassages.
 21. The fuel cell according to claim 16, wherein theoxygen-containing gas supplied to and partially consumed in theelectrolyte electrode assemblies is discharged as an exhaustoxygen-containing gas through the oxygen-containing gas channel to theexhaust gas discharge passage.
 22. The fuel cell according to claim 1,wherein the fuel cell is a solid oxide fuel cell.